battery_temp: initial commit.

Simple script to read battery temperature and return
degrees Celsius if readable, 'error' if unreadable or 'unknown'
otherwise.

Signed-off-by: Todd Broch <tbroch@chromium.org>

BRANCH=none
BUG=chromium:816744
TEST=manual, run on following duts with return values of:
  elm: <degC>
  eve: <degC>
  expresso: <degC>
  heli: <degC>
  peppy: 'unknown'
  samus: <degC>
  squawks: <degC> | 'error' if battery removed.

Change-Id: I3147ceb3ea0e0a22c08617e212c66d0c3e58b300
Reviewed-on: https://chromium-review.googlesource.com/982815
Commit-Ready: Todd Broch <tbroch@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@google.com>

util/battery_temp

@@ -0,0 +1,56 @@
+#!/bin/bash
+# Copyright 2018 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+#
+# Description: Read and output temperature of device's primary battery in
+# degrees Celsius.
+#
+# TODO(tbroch) revisit for detachables with multiple batteries.
+
+# Read battery temperature from sysfs power_supply and return in degC.
+batt_temp_sysfs() {
+    local temp=""
+
+    for psdir in /sys/class/power_supply/* ; do
+        if [[ -e "${psdir}/temp" ]] ; then
+            pstype=$(cat $psdir/type)
+            if [[ "${pstype}" -eq "Battery" ]] ; then
+                temp=$(bc <<< "scale=2; $(cat ${psdir}/temp)/10")
+                break
+            fi
+        fi
+    done
+    echo ${temp}
+}
+
+# Read battery temperature from EC and return in degC.
+batt_temp_ec() {
+    local temp=""
+
+    local sensor_str=$(ectool tempsinfo all 2>/dev/null | grep Battery)
+    if [[ $? -eq 0 ]] && [[ ! -z "${sensor_str}" ]] ; then
+        local idx=$(echo ${sensor_str} | cut -d: -f1)
+        # ectool temps <idx> looks like 'Reading temperature...298 K'
+        temp_str=$(ectool temps ${idx})
+        temp="${temp_str//[!0-9]/}"
+        if [[ -z "${temp}" ]] ; then
+            temp="error"
+        else
+            temp=$(bc <<< "scale=2; ${temp} - 273.15")
+        fi
+    fi
+    echo $temp
+}
+
+# Main
+TEMP_DEGC=$(batt_temp_sysfs)
+if [[ -z "${TEMP_DEGC}" ]] ; then
+    TEMP_DEGC=$(batt_temp_ec)
+fi
+
+if [[ -z "${TEMP_DEGC}" ]] ; then
+    echo "unknown"
+else
+    echo ${TEMP_DEGC}
+fi